1. Field of the Invention
The present invention relates in general to a projector with adjustable brightness and uniformity.
2. Description of the Related Art
The portable digital projectors commercially available in the market include DLP (Digital Light Processing) projectors and LCD panel (Liquid Crystal Display panel) projectors. The two kinds of projectors have a common defect: either the picture brightness or the uniformity of brightness produced by the projectors is poor. FIGS. 1A and 1B depict this conundrum. In FIG. 1A, the brightness on the central portion of a projection surface (xy-plane) 100 is strong but the brightness on the side portions of the projection surface 100 is weak. That is, the brightness is good but the uniformity of brightness is poor. In FIG. 1B, the uniformity of brightness on the projection surface 100 is greatly improved. However, the brightness on the central portion of the projection surface 100 is weakened.
Generally, a portable digital projector is connected to a computer for a user to make a briefing, or is connected to an image output device such as a video tape recorder, a VCD player, an LD player or a DVD player to show films. In the case of a briefing, the user prefers the brightness rather than the uniformity of brightness because the briefing room generally is not dark enough. In the case of showing films, however, the user prefers the uniformity of brightness rather than the brightness so as to produce clear and beautiful pictures. Taking both cases into consideration, the projector manufacturers generally compromise between the brightness and the uniformity in design. As a result, the projection picture produced by the projector is not bright enough when the user makes a briefing, and the uniformity of brightness is not good enough when the user watches a film.